Current flat panel displays such as LCD, LED, and electrophoretic displays generally include backplane circuitry for operation of picture elements or pixels that are arranged in rows and columns in the display. The backplane may, for example, implement an active matrix that is able to refresh an entire row of pixels at once. Such backplanes generally include an array of thin film transistors (TFTs), where one or more TFTs have their source or drain coupled to respective electrodes in a corresponding pixel. The TFTs for a row of pixels have gates coupled to a gate or row line corresponding to the row, and the TFTs corresponding to a column of pixels generally have their drains or sources coupled to a data or column line corresponding to the column.
Conventional integrated circuit processing techniques such as precision photolithography can be difficult to employ for fabrication of a backplane for a large display because of the large area covered and because materials commonly employed in the displays are flexible and difficult to keep flat over the large area. In general, fabricating a TFT requires at least three masking levels, and more masking levels may be needed to form the backplane of a display. Accurately aligning mask patterns against each level is difficult for flexible substrates which have poor dimension stability.
U.S. Pat. No. 7,202,179, entitled “Method of forming at least one Thin Film Device” describes fabrication processes using three-dimensional (3D) templates that can be imprinted on a large area such as the area of a flat panel display. Using these techniques, a 3D template is imprinted on top of a multilayer stack to be patterned. The 3D template generally has multiple levels, with each level corresponding to different thicknesses of the 3D template and a different underlying layer to be patterned. An anisotropic etching process can then thin the 3D template and etch through portions of the underlying layers that become exposed. The process etches deeper into the underlying layers where the 3D template was thinner. For example, the etch process may etch down through the bottom layer of a multi-layer stack where the 3D template was thinnest, but the other levels of the 3D template are thick enough that the portions of the bottom layer under other levels of the 3D template remain. After the process is complete, each layer of the multilayer stack is left with a pattern corresponding to the areas where the 3D template and overlying layers of the multilayer stack were thick enough to protect the layer.
An advantage of using a 3D template in manufacture of a backplane for a display is that the multiple layers of the stack that are patterned with a single 3D template are automatically aligned with each other. Further, roll-to-roll imprinting techniques can cover the large area of a display. Etching multiple layers with a 3D template does have difficulty when producing signal lines or other structures that cross in different layers. For example, the row lines and data lines of a conventional backplane cross each other, so that a conventional fabrication process using 3D templates requires an undercut process (e.g., a wet etch process) to remove portions of the row or data line that are under portions of the data or row lines.
In order to realize high yield manufacturing processes, methods for fabricating a backplane for a display that efficiently align overlying layers and that provide low defect rates are desired.